Image processing method, image processing apparatus, and storage medium

ABSTRACT

Mapping conversion to absorb differences of shapes of color reproduction gamuts and also keep gradation is provided. Namely, an image processing method by which a color signal located within a first color reproduction gamut represented by a first color system is subjected to mapping conversion into a color signal located within a second color reproduction gamut represented by the first color system, wherein a locus of a change of color in the first color reproduction gamut is represented by a curve, mapping is performed to the curve, and the mapping conversion is performed on the basis of relation of the curves before and after the mapping.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a technical field in which acolor signal located within a first color reproduction gamut (or range)represented by a first color system is subjected to mapping conversioninto a color signal located within a second color reproduction gamutrepresented by the first color system.

[0003] 2. Related Background Art

[0004] In recent years, as a personal computer and a work stationspread, DTP (desktop publishing) and CAD (computer-aided design) havecome to be widely used. Thus, color reproduction technique by which acolor represented on a monitor by the computer is actually reproduced byusing a coloring agent becomes important. For example, in the DTP, acomputer system which includes at least a color monitor and a colorprinter creates, edits and processes a color image on the color monitor,and then outputs the obtained color image by the color printer. Here, auser strongly wishes that the color image on the monitor sensuously andthe printer output image are matched.

[0005] However, in the color reproduction technique, difficulty isattended so that the color image on the monitor and the printer outputimage may be matched, because of the following reasons.

[0006] The color monitor represents the color image by generating lightof a specific frequency with use of a fluorescent body. On the otherhand, the color printer absorbs light of a specific frequency by usingink or the like, and represents the color image based on remainingreflection light. Thus, since an image display form of the color monitoris different from an image display form of the color printer, the colorreproduction gamut of the color monitor is highly different from thecolor reproduction gamut of the color printer. Further, even in thecolor monitors, the color reproduction gamut is different among a liquidcrystal monitor, a CRT (cathode-ray tube) of electron-gun type, and aplasma monitor. Also, even in the color printers, the color reproductiongamut is different in accordance with difference of sheet quality,difference of ink usage quantity, and the like. For this reason, it isimpossible to completely match the color of the image on the colormonitor with the color of the image output from the color printercalorimetrically. It is also impossible to completely match the colorsof the images on the plural kinds of sheets output from the plural kindsof color printers colorimetrically. Therefore, when a person perceivesthe displayed color image on each output medium, he feels seriousdistinction about each output image.

[0007] Here, as technique to absorb perceivable distinction on thedisplayed color image and perceivably match the displayed images amongthe display media of which the reproduction gamuts are different fromothers, there is gamut mapping technique that one color reproductiongamut is mapped into another color reproduction gamut by using a uniformcolor system. As one example of the gamut mapping technique, there isthe technique that, in the uniform color system, linear mapping isperformed in a lightness-chroma dimension for each hue. According tothis technique, a monitor color reproduction gamut as schematicallyshown in FIG. 27 is mapped into a printer color reproduction gamut asschematically indicated by the dotted line in FIG. 28.

[0008] However, the image which was corrected by the linear mapping andthen output might be undesirable perceivably. Namely, the differencebetween the shape of the monitor color reproduction gamut and the shapeof the printer color reproduction gamut causes unnaturalness.

[0009] Here, the difference between the shape of the monitor colorreproduction gamut and the shape of the printer color reproduction gamutwill be simply explained. For example, FIG. 29 schematically shows themonitor and printer color reproduction gamuts in a green hue. Namely, inFIG. 29, the printer color reproduction gamut is indicated by the solidline, while the monitor color reproduction gamut is indicated by thedotted line. As apparent from FIG. 29, in the green hue, the monitorcolor reproduction gamut is nonsimilar to the printer color reproductiongamut, and thus the shape of the monitor color reproduction gamut isquite different from the shape of the printer color reproduction gamut.Then, FIG. 30 schematically shows the monitor and printer colorreproduction gamuts in a red hue. In FIG. 30, the monitor colorreproduction gamut is indicated by the solid line, while the printercolor reproduction gamut is indicated by the dotted line. As apparentfrom FIG. 30, in the red hue, the shape of the monitor colorreproduction gamut is relatively similar to the shape of the printercolor reproduction gamut.

[0010] In order to solve the above problem, nonlinear gamut mapping tokeep chroma in the low-chroma part and lightness in theintermediate-lightness part and also absorb the difference between theshape of the monitor color reproduction gamut and the shape of theprinter color reproduction gamut is efficient.

[0011] As the nonlinear gamut mapping, a method of superposing one- tothree-dimensional mapping has been proposed.

[0012] However, in this nonlinear gamut mapping, there is room ofimprovement in the point of gradation. Namely, in case of superposingthe one- to three-dimensional mapping according to the conventionalgamut mapping method, each mapping is different from others because ofchromaticity, hue and the like of the mapping-target color. Thus, evenif there is no problem in the individual mapping either, a problem mightoccur in the gradation as a result of superposing each mapping.

[0013] Here, it should be noted that the term “gradation” is used forthe meaning of a proper change rate in a case where color changesaccording to a certain rule. Further, the operation to keep thegradation corresponds to the operation to properly keep the change rate.Next, FIGS. 31A and 31B will be briefly explained. In a case where aproper change rate has varied greatly as shown by the part enclosed withthe circle in FIG. 31A, in general, such the variation frequently causesa pseudo contour and the like though it is dependent on conditions suchas hue, chroma and the like. On the other hand, in a case where a properchange rate can be kept as shown in FIG. 31B, a perceivable problem doesnot occur easily.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to absorb a difference inshapes of color reproduction gamuts, provide mapping conversion askeeping gradation, suppress a pseudo contour in an output image, andobtain a high-quality output image.

[0015] In order to achieve the above object, the present inventionprovides an image processing method by which a color signal locatedwithin a first color reproduction gamut represented by a first colorsystem is subjected to mapping conversion into a color signal locatedwithin a second color reproduction gamut represented by the first colorsystem, wherein

[0016] a locus of a change of color in the first color reproductiongamut is represented by a curve, mapping is performed to the curve, andthe mapping conversion is performed on the basis of relation of thecurves before and after the mapping.

[0017] Other objects and features of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a block diagram showing a system structure of a colorsignal conversion device according to the first embodiment of thepresent invention;

[0019]FIG. 2 is a block diagram showing a structure of the color signalconversion device according to the first embodiment;

[0020]FIG. 3 is a flow chart showing a mapping operation of a colorgamut mapping device 207 in the first embodiment;

[0021]FIG. 4 is a schematic diagram showing loci of a surface samplepoint before and after the mapping on a green face;

[0022]FIG. 5 is a flow chart showing a mapping operation in a step 303of FIG. 3 in the second embodiment of the present invention;

[0023]FIG. 6 is a flow chart showing a mapping operation in a step 502of FIG. 5 in the second embodiment;

[0024]FIG. 7 is a schematic diagram showing spatial relation of color Mand color Bm;

[0025]FIG. 8 is a diagram showing an example of a chroma input/outputfunction for achieving nonlinear mapping of a chroma component;

[0026]FIG. 9 is a diagram showing an example of a lightness input/outputfunction for achieving nonlinear mapping of a lightness component;

[0027]FIG. 10 is a schematic diagram showing a state of mapping on agreen face;

[0028]FIG. 11 is a flow chart showing a mapping operation in a step 504of FIG. 5 in the second embodiment;

[0029]FIG. 12 is a schematic diagram showing spatial relations ofrespective lines used in steps 1101 to 1106;

[0030]FIGS. 13A and 13B are diagrams showing an example of the lightnessinput/output function for achieving the nonlinear mapping of thelightness component;

[0031]FIG. 14 is a schematic diagram showing a state of mapping until alightness adjustment mapping operation in the step 504, on the greenface;

[0032]FIG. 15 is a flow chart showing the mapping operation in the step504 of FIG. 5 in the second embodiment;

[0033]FIG. 16 is a schematic diagram showing spatial relations ofrespective colors obtained in steps 1501 to 1504;

[0034]FIGS. 17A and 17B are diagrams showing an example of the chromainput/output function for achieving the nonlinear mapping of the chromacomponent;

[0035]FIG. 18 is a schematic diagram showing a state of the mapping onthe green face;

[0036]FIG. 19 is a schematic diagram showing surface gradation linesbefore the mapping;

[0037]FIG. 20 is a schematic diagram showing the surface gradation linesafter the mapping;

[0038]FIG. 21 is a schematic diagram showing internal gradation linesbefore the mapping;

[0039]FIG. 22 is a schematic diagram showing the internal gradationlines after the mapping;

[0040]FIG. 23 is a schematic diagram showing the internal gradationlines before the mapping;

[0041]FIG. 24 is a schematic diagram showing the internal gradationlines after the mapping;

[0042]FIG. 25 is a table showing values capable of being taken as R, Gand B values;

[0043]FIG. 26 is a schematic diagram showing distribution of surfacesample points and internal sample points on a sectional plane in an RGBcolor space;

[0044]FIG. 27 is a schematic diagram showing a monitor colorreproduction gamut in a green hue;

[0045]FIG. 28 is a schematic diagram showing an example of gamutmapping;

[0046]FIG. 29 is a schematic diagram showing a monitor colorreproduction gamut and a printer color reproduction gamut in the greenhue;

[0047]FIG. 30 is a schematic diagram showing a monitor colorreproduction gamut and a printer color reproduction gamut in the redhue; and

[0048]FIGS. 31A and 31B are schematic diagrams for explaining gradation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] First Embodiment

[0050]FIG. 1 is a block diagram showing a system structure of a colorsignal conversion device according to the first embodiment.

[0051] In FIG. 1, numeral 101 denotes a CPU (central processing unit),numeral 102 denotes a main memory, numeral 103 denotes a SCSI (smallcomputer system interface), numeral 104 denotes a network I/F(interface), numeral 105 denotes an HDD (hard disk drive), numeral 106denotes a graphic accelerator, numeral 107 denotes a color monitor,numeral 108 denotes a color signal conversion device, numeral 109denotes a color printer, numeral 110 denotes a keyboard/mousecontroller, numeral 111 denotes a keyboard, numeral 112 denotes a mouse,numeral 113 denotes a LAN (local area network), and numeral 114 denotesa PCI (peripheral component interface) bus.

[0052] Image data stored in the HDD 105 is transferred to the mainmemory 102 through the SCSI 103 and the PCI bus 114, in response to aninstruction from the CPU 101. Further, image data stored in a serverconnected to the LAN 113 or image data on the Internet is transferred tothe main memory 102 through the network I/F 104 and the PCI bus 114, inresponse to an instruction from the CPU 101.

[0053] The image data stored in the main memory 102 is transferred tothe graphic accelerator 106 through the PCI bus 114 in response to aninstruction from the CPU 101. The transferred image data is D/A(digital-to-analog) converted by the graphic accelerator 106, theobtained analog data is then transmitted to the color monitor 107through a display cable, and the image data is displayed on the colormonitor 107. Here, if a user instructs to output the image data storedin the main memory 102 through the color printer 109, the CPU 101 firsttransfers color reproduction gamut information of the proper colormonitor and color reproduction gamut information of the proper colorprinter from the HDD 105 to the main memory 102, and the CPU 101 furthertransfers these two kinds of color reproduction gamut information to thecolor signal conversion device 108. Besides, the CPU 101 instructs thecolor signal conversion device 108 to perform initialization for dataconversion from R (red), G (green) and B (blue) image data into C(cyan), M (magenta), Y (yellow) and K (black) image data. Theinitialization will be later described in detail. After theinitialization ended, the R, G and B image data stored in the mainmemory 102 are transferred to the color signal conversion device 108through the PCI bus 114 in response to an instruction from the CPU 101.The color signal conversion device 108 performs color signal conversionto the R, G and B image data on the basis of a result of gamut mapping,and then transmits the C, M, Y and K image data being the convertedresults to the color printer 109. As a result of such a series ofoperations, the C, M, Y and K image data are output from the colorprinter 109.

[0054]FIG. 2 is a block diagram showing a structure of the color signalconversion device 108.

[0055] In FIG. 2, numeral 201 denotes an LUT (look-up table) creationunit in which respective devices operate according to designatedprocedures to create an LUT for converting the R, G and B image datainto the C, M, Y and K image data. Numeral 202 denotes a RAM(random-access memory) in which the LUT created by the LUT creation unit201 is stored. Numeral 203 denotes an interpolation device in which theC, M, Y and K image data to be output with respect to the input R, G andB image data are calculated through an interpolation operation using theLUT stored in the RAM 202. Numeral 211 denotes a terminal through whichthe R, G and B image data stored in the main memory are input in an RGBdata format according to a raster scan method, and numeral 212 denotes aterminal through which the C, M, Y and K image data corresponding to theinput R, G and B image data are output to the color printer.

[0056] Next, the internal structure of the LUT creation unit 201 will beexplained. Numeral 209 denotes a terminal through which informationrepresenting the printer color reproduction gamut is input, and numeral210 denotes a terminal through which information representing themonitor color reproduction gamut is input. Numeral 204 denotes a monitorcolor gamut storage device which stores the input monitor colorreproduction gamut information, and numeral 205 denotes a printer colorgamut storage device which stores the input printer color reproductiongamut information. Numeral 206 denotes a mapping parameter calculationdevice which calculates compression parameters necessary in alater-described color gamut mapping device 207, by referring to theprinter color reproduction gamut information and the monitor colorreproduction gamut information. Numeral 207 denotes the color gamutmapping device which maps the monitor color reproduction gamut into theprinter color reproduction gamut by referring the monitor colorreproduction gamut information and the printer color reproduction gamutinformation. Hereinafter, the result of the mapping is called a mappingcolor reproduction gamut. Numeral 208 denotes an LUT creation devicewhich creates the LUT for converting the R, G and B image data into theC, M, Y and K image data, by referring to relation between the monitorcolor reproduction gamut and the mapping color reproduction gamut, theR, G and B image data for outputting a predetermined color on themonitor, and the C, M, Y and K image data for outputting a predeterminedcolor on the printer.

[0057] Next, the operation of the LUT creation unit 201 will beexplained. It should be noted that, although an L*a*b* color space isused as a uniform color system in the mapping operation of the LUTcreation unit 201 according to the present embodiment, another kind ofuniform color system may be used.

[0058] First, the color reproduction gamut information of the colormonitor and the color reproduction gamut information of the colorprinter are transmitted in response to an instruction from the CPU 101.The transmitted color reproduction gamut information of the colormonitor is stored as the monitor color reproduction gamut information inthe monitor color gamut storage device 204 in the LUT creation unit 201,and the transmitted color reproduction gamut information of the colorprinter is stored as the printer color reproduction gamut information inthe printer color gamut storage device 205 in the LUT creation unit 201.After the transmission of the information ended, it is instructed by theCPU 101 to perform initialization for color signal conversion. If suchan instruction is received by the color signal conversion device 108,the internal structure of the LUT creation unit 201 operates as follows.First, the mapping parameter calculation device 206 operates tocalculate the various parameters necessary for the color gamut mappingdevice 207.

[0059] After the calculation of the parameters ended, the color gamutmapping device 207 operates to map the monitor color reproduction gamutinto the printer color reproduction gamut in the uniform color system.It should be noted that, in the present embodiment, the color gamutmapping device 207 performs the mapping operation according to a flowchart shown in FIG. 3, and such the mapping operation will be describedlater.

[0060] Next, the LUT creation device 208 creates the LUT for convertingthe R, G and B image data into the C, M, Y and K image data by referringto the mapping color reproduction gamut being the final mapping result,and then writes the created LUT in the RAM 202. After such a series ofoperations as above ended, the LUT creation device 208 notifies the CPU101 of the fact that the initialization ended.

[0061] In the following, the operation of the color gamut mapping device207 will be explained with reference to the flow chart shown in FIG. 3.It should be noted that, in the explanation of the flow chart in FIG. 3,a consecutive locus by which a certain color and a certain color areconnected is called a gradation line.

[0062] In a step 301, sample points to define the mapping of the colorgamut is determined. The determined sample points include surface samplepoints to define the mapping on the surface of the monitor colorreproduction gamut and internal sample points to define the mapping inthe monitor color reproduction gamut.

[0063] In a step 302, with respect to the surface sample points, it isdetermined where the mapping should be performed within the printercolor reproduction gamut. Here, it should be noted that the mappingresult of the surface sample points is not necessarily located on thesurface of the printer color reproduction gamut. In a step 303, withrespect to the internal sample points, it is determined where themapping should be performed within the printer color reproduction gamut.In this case, it should be noted that the mapping is controlled suchthat the mapping result of the internal sample points is sure to belocated inside the printer color reproduction gamut.

[0064] In a step 304, a gradation line (called a surface gradation linehereinafter) connecting the predetermined two different surface samplepoints is defined. Then, in a step 305, with respect to the surfacegradation line, it is determined where the mapping should be performedwithin the printer color reproduction gamut. In this case, it should benoted that the mapping is controlled such that the mapping result of thesurface gradation line is sure to be the consecutive locus. Further, itshould be noted that the mapping result of the surface gradation line isnot necessarily located on the surface of the printer color reproductiongamut.

[0065] In a step 306, a gradation line (called an internal gradationline hereinafter) connecting the predetermined two different internalsample points is defined. Then, in a step 307, with respect to theinternal gradation line, it is determined where the mapping should beperformed within the printer color reproduction gamut. In this case, itshould be noted that the mapping is controlled such that the mappingresult of the internal gradation line is sure to be the consecutivelocus and to be located inside the printer color reproduction gamut.

[0066] Finally, in a step 308, with respect to the color desired torepresent the mapping color reproduction gamut, the mapping result ofthe monitor color reproduction gamut into the mapping color reproductiongamut is calculated on the basis of the surface and internal gradationlines.

[0067] In the present embodiment, following two methods are adopted toobtain the mapping result. One is the method of first calculatinginternal divided ratio of the gradation line for the desired colorbefore the mapping, and then obtaining the mapping result from thegradation line after the mapping in accordance with the calculatedinternal divided ratio, and the other is the method of first calculatingangle ratio on the gradation line for the desired color before themapping, and then obtaining the mapping result from the gradation lineafter the mapping in accordance with the calculated angle ratio.

[0068] In order to represent the surface gradation line and the internalgradation line, various spline curves such as a B-Spline curve, a one-or more-dimensional Spline curve, etc., a Bezier curve, and the like canbe used.

[0069] According to the present embodiment, a proper change rate in acase where color varies according to a certain rule in the colorreproduction gamut before the mapping can be preserved, whereby thegradation can be well maintained. Further, according to the presentembodiment, since the various spline curves can be used to represent thesurface gradation line and the internal gradation line, free and easycontrol can be performed. Further, since various spline technique andcurve fitting technique in a 3D-CAD (three-dimensional computer-aideddesign) and the like can be applied, extendibility is abundant.

[0070] Further, according to the present embodiment, in addition to themapping from the monitor color reproduction gamut into the printer colorreproduction gamut, various applications such as mapping from theprinter color reproduction gamut into another different printer colorreproduction gamut, mapping from the monitor color reproduction gamutinto another different monitor color reproduction gamut, and the likecan be performed.

[0071] In the present embodiment, the restraint condition to preservethe change rate results in the technique of the mapping by “curve”.Namely, the locus of the change of the color in the color reproductiongamut being the mapping origin is represented by using the curve, andthe mapping is performed such that the change rate of this curve ismaintained, whereby the change rate is preserved.

[0072] According to the present invention, the proper change rate in thecase where the color varies according to the certain rule in the colorreproduction gamut before the mapping can be preserved, whereby thegradation can be well maintained, and the gamut mapping to absorb thedifference in shapes of the monitor color reproduction gamut and theprinter color reproduction gamut can be performed. Therefore, in case ofoutputting the image corrected by the gamut mapping, a problem on sightsuch as a pseudo contour or the like can be greatly decreased, and alsothe images in which the sights of colors are matched with others can beobtained.

[0073] Second Embodiment

[0074] In the first embodiment, the color gamut mapping with very highfreedom degree is possible. On the other hand, since the control itemsextend to be multiplex, the load for color design becomes heavy. Forexample, since there are huge freedom degrees even in only setting thesurface sample points and the internal sample points, to adjust themrequires labor. Thus, in the second embodiment, a method of reducing thelabor in the color design by daring to add limitations to the surfacesample points and the internal sample points is proposed.

[0075] It should be noted that the second embodiment is obtained bymodifying the operation algorithm of the color gamut mapping device 207in the first embodiment. For this reason, the operation explanationoverlapping with the operation explanation in the first embodiment isomitted, and only the operation algorithm of the color gamut mappingdevice 207 will be explained.

[0076] The operation of the color gamut mapping device 207 will beexplained with reference to the flow chart shown in FIG. 3. Hereinafter,each step of the flow chart will be described in detail.

[0077] To determine the sample points in the step 301 will be describedin detail.

[0078] In case of determining the surface sample points and the internalsample points, later-described restraint conditions are defined, andsample points distributed on six faces of a red face, a green face, ablue face, a cyan face, a magenta face and an yellow face are thought.Of course, to control the mapping, there is no problem even if a samplepoint which does not satisfy the later-described restraint conditionsand is not distributed on the above six faces exists.

[0079] The restraint condition to the sample points distributed on thesix faces is not defined in an L*a*b* color space but defined in an RGBcolor space. The conversion relation between the RGB color space and theL*a*b* color space has been stored in the monitor color gamut storagedevice 204 storing the monitor color reproduction gamut, and the colorgamut mapping device 207 can always use the stored conversion relation.It should be noted that the color reproduction gamut in the RGB colorspace is defined by 0≦R≦255, 0≦G≦255, and 0≦B≦255.

[0080] First, the condition for the surface sample point will bedescribed. Namely, the condition for the sample point is to satisfy anyof following 12 conditions.

G=B=0, 0≦R≦255  condition A1)

0≦G=B≦255, R=255  condition A2)

[0081] If either one of these two conditions is satisfied, the samplepoint is located on the red face and on the surface of the monitor colorreproduction gamut.

R=B=0, 0≦G≦255  condition A3)

0≦R=B≦255, G=255  condition A4)

[0082] If either one of these two conditions is satisfied, the samplepoint is located on the green face and on the surface of the monitorcolor reproduction gamut.

R=G=0, 0≦B≦255  condition A5)

0≦R=G≦255, B=255  condition A6)

[0083] If either one of these two conditions is satisfied, the samplepoint is located on the blue face and on the surface of the monitorcolor reproduction gamut.

R=0, 0≦G=B≦255  condition A7)

0≦R≦255, G=B=255  condition A8)

[0084] If either one of these two conditions is satisfied, the samplepoint is located on the cyan face and on the surface of the monitorcolor reproduction gamut.

G=0, 0≦R=B≦255  condition A9)

0≦G≦255, R=B=255  condition A10)

[0085] If either one of these two conditions is satisfied, the samplepoint is located on the magenta face and on the surface of the monitorcolor reproduction gamut.

B=0, 0≦R=G≦255  condition A11)

0≦B≦255, R=G=255  condition A12)

[0086] If either one of these two conditions is satisfied, the samplepoint is located on the yellow face and on the surface of the colorreproduction gamut.

[0087] Next, the condition for the internal sample point will bedescribed. Namely, the condition for the internal sample point is tosatisfy any of following six conditions.

G=B≦R, 0<R<255  condition B1)

[0088] If this condition is satisfied, the sample point is located onthe red face and inside the monitor color reproduction gamut.

R=B≦G, 0<G<255  condition B2)

[0089] If this condition is satisfied, the sample point is located onthe green face and inside the monitor color reproduction gamut.

R=G≦B, 0<B<255  condition B3)

[0090] If this condition is satisfied, the sample point is located onthe blue face and inside the monitor color reproduction gamut.

R≦G=B, 0<G=B<255  condition B4)

[0091] If this condition is satisfied, the sample point is located onthe cyan face and inside the monitor color reproduction gamut.

G≦R=B, 0<R=B<255  condition B5)

[0092] If this condition is satisfied, the sample point is located onthe magenta face and inside the monitor color reproduction gamut.

B≦R=G, 0<R=G<255  condition B6)

[0093] If this condition is satisfied, the sample point is located onthe yellow face and inside the monitor color reproduction gamut.

[0094] Further, in the mapping calculation of the surface sample pointsin the step 302, a next restraint condition is newly added. Namely, withrespect to the surface sample point which satisfies any one of theconditions A1, A3, A5, A7, A9 and A11, the mapping is surely performedon the surface of the printer color reproduction gamut. However, withrespect to the surface sample point which satisfies any one of theconditions A2, A4, A6, A8, A10 and A12, the mapping might be performedinside the printer color reproduction gamut.

[0095] Here, loci of the surface sample point before and after themapping on the green face is schematically shown in FIG. 4 as an exampleof the mapping in the step 302. In FIG. 4, the alternate short and longdashed line represents the locus of the surface sample point obtained incase of satisfying either the condition A3 or the condition A4, and thesolid line represents the locus obtained in case of mapping the surfacesample point. The dotted line represents an example of the locusobtained in the case where all the surface sample points are mapped intothe surface of the printer color reproduction gamut.

[0096] In the following explanation, a chroma-lightness locus (i.e., thelocus represented by the alternate short and long dashed line in FIG. 4)of the surface sample point in case of satisfying either the conditionA3 or the condition A4 is called a monitor green line. Further, achroma-lightness locus (i.e., the locus represented by the solid line inFIG. 4) obtained by mapping the surface sample point is called a mappedgreen line.

[0097] Further, according to the above expression manner, achroma-lightness locus of the surface sample point in case of satisfyingeither the condition A1 or A2 is called a monitor red line, achroma-lightness locus of the surface sample point in case of satisfyingeither the condition A5 or A6 is called a monitor blue line, achroma-lightness locus of the surface sample point in case of satisfyingeither the condition A7 or A8 is called a monitor cyan line, achroma-lightness locus of the surface sample point in case of satisfyingeither the condition A9 or A10 is called a monitor magenta line, and achroma-lightness locus of the surface sample point in case of satisfyingeither the condition A11 or A12 is called a monitor yellow line. In caseof not especially sticking to hue, such the locus is called a monitorline. Further, corresponding chroma-lightness loci obtained by mappingthe surface sample point are respectively called a mapped red line, amapped blue line, a mapped cyan line, a mapped magenta line and a mappedyellow line. In case of not especially sticking to hue, such the locusis called a mapped line.

[0098] Next, the process in the step 303 will be explained withreference to a flow chart of FIG. 5.

[0099] It should be noted that the present embodiment is directed to thealgorithm on the premise that the mapping to be originally performed ona three-dimensional space has been reduced to the mapping on atwo-dimensional space.

[0100] In a step 501, a lightness component L_(S), a chroma componentC_(S) and a hue component H_(S) are separated from an internal samplepoint S. In a step 502, the mapping is performed only for the separatedlight component L_(S), and in a step 503, the mapping is performed onlyfor the separated chroma component C_(S).

[0101] In the above steps, a boundary of the area to which the internalsample point can be mapped for the red face is called a firstintermediate mapped red line, such a boundary for the green face iscalled a first intermediate mapped green line, such a boundary for theblue face is called a first intermediate mapped blue line, such aboundary for the cyan face is called a first intermediate mapped cyanline, such a boundary for the magenta face is called a firstintermediate mapped magenta line, and such a boundary for the yellowface is called a first intermediate mapped yellow line. In case of notespecially sticking to hue, such a boundary is called a firstintermediate mapped line.

[0102] As one example, FIG. 10 schematically shows relation between themonitor green line (the locus represented by the alternate short andlong dashed line) and the first intermediate mapped green line (thelocus represented by the solid line) on the green face.

[0103] In a step 504, in order to adjust the lightness, the mapping ofthe lightness is again performed as keeping the chroma constant.

[0104] In this step, a boundary of the area to which the internal samplepoint can be mapped for the red face is called a second intermediatemapped red line, such a boundary for the green face is called a secondintermediate mapped green line, such a boundary for the blue face iscalled a second intermediate mapped blue line, such a boundary for thecyan face is called a second intermediate mapped cyan line, such aboundary for the magenta face is called a second intermediate mappedmagenta line, and such a boundary for the yellow face is called a secondintermediate mapped yellow line. In case of not especially sticking tohue, such a boundary is called a second intermediate mapped line.

[0105] In a case where the mapped line has been previously given, if thefirst intermediate mapped line is determined, the locus of the secondintermediate mapped line is determined biuniquely based on the relationbetween the first intermediate mapped line and the mapped line. Namely,when only the lightness component is mapped for the first intermediatemapped line, the second intermediate mapped line is given. When only thechroma component is mapped for the second intermediate mapped line, themapped line is given. Therefore, if the chroma component of the firstintermediate mapped line is combined with the lightness component of themapped line, the second intermediate mapped line is given.

[0106] The present embodiment is explained on the premise that themapped line has been previously given.

[0107] Here, FIG. 14 schematically shows relation between the firstintermediate mapped green line and the second intermediate mapped greenline on the green face.

[0108] In a step 505, in order to match the final mapping area with themapped green line, the mapping of the chroma is performed as keeping thelightness constant. By this step, the mapping area of the internalsample points represented by the second intermediate mapped line ismapped into the mapping area represented by the mapped line. Here, FIG.18 schematically shows relation among the first intermediate mappedgreen line, the second intermediate mapped green line and the mappedgreen line on the green face.

[0109] In the following, the lightness mapping operation in the step 502will be explained in detail.

[0110] An input/output function is controlled to preserve, forintermediate lightness, such the lightness. In the vicinities of maximumlightness and minimum lightness, the input/output function is controlledto lower the differentiation value of the input/output function, i.e.,to increase a compression ratio. Further, in order to prevent that apseudo contour or the like appears, the input/output function iscontrolled such that at least a first differentiation becomes continuousin all the points (i.e., C1 continuousness). FIG. 9 shows an example ofthe mapping of the lightness component according to the presentembodiment. It should be noted that control parameters in this mappinghave been previously set by the mapping parameter calculation device206.

[0111] In the following, the chroma mapping operation in the step 503will be explained in detail with reference to a flow chart shown in FIG.6.

[0112] In a step 601, a contour chroma compression ratio Rb in hue ofthe color M being the mapping target is obtained by the mappingparameter calculation device 206. The hue of the color M belongs to anyof the red face, the green face, the blue face, the cyan face, themagenta face and the yellow face, and the contour chroma compressionratio Rb is determined for each of these six faces.

[0113] In a step 602, a color Bm at the boundary of the monitor line inthe lightness same as the color M is calculated. FIG. 7 schematicallyshows the relation between the color M and the color Bm. In FIG. 7, thesolid line represents the monitor line, and the dotted lineschematically represents how the contour of the monitor line is mappedin the chroma mapping operation of the step 503.

[0114] In a step 603, a ratio R is calculated from chroma Cm of thecolor M and chroma Cbm of the color Bm, as R=Cm/Cbm. Next, in a step604, a chroma input/output function g(•) for chroma mapping is obtainedby the mapping parameter calculation device 206.

[0115] In a step 605, the chroma mapping is performed by using afollowing expression, on the basis of the parameters calculated andobtained as above. It should be noted that symbol Cm_(—mapped) denotesthe chroma after the mapping.

Cm _(—mapped) =Cbm×g(R)

[0116] Here, the chroma input/output function g(•) has followingconditions. Namely, the support of g(•) is [0, 1], g(•) increasesmonotonously, g(0)=0, g(1)=Rb, g(•) is at least C1 continuousness,G′(0)=1, G′(1)=γ (γ>0, γ is a constant to control the compression, γ isdetermined for each hue, and γ varies in inverse proportion to Rb), andg′(x)≠0 (0≦x≦1).

[0117] The chroma input/output function g(•) can be shown as a schematicdiagram in FIG. 8. Namely, as the chroma becomes lower, the chroma ispreserved more. Further, as the chroma becomes higher, the chroma iscompressed at a higher compression ratio. Further, since theinput/output function is at least the C1 continuousness, the change rateof the chroma smoothly varies, whereby it is prevented that the pseudocontour or the like appears.

[0118] By the lightness mapping operation in the step 502 and the chromamapping operation in the step 503 as described above, the areasurrounded by the monitor line is mapped into the area surrounded by thefirst intermediate mapped line. FIG. 10 shows the state of the mappingon the green face by way of example. In FIG. 10, the alternate short andlong dashed line represents the monitor green line and thechroma-lightness loci belonging to the green face in the monitor colorreproduction gamut, the solid line represents the first intermediatemapped green line and the mapping result of the chroma-lightness loci,and the dotted line represents the mapped green line.

[0119] In the following, the lightness adjustment mapping operation inthe step 504 will be explained with reference to a flow chart shown inFIG. 11.

[0120] In a step 1101, an upper boundary Bu of the first intermediatemapped line in the chroma same as a color M1 is calculated. In a step1102, a lower boundary B1 of the first intermediate mapped line in thechroma same as the color M1 is calculated. FIG. 12 shows an example ofthe relation among the color M1, the upper boundary Bu and the lowerboundary B1 on the green face. In FIG. 12, the solid line represents thefirst intermediate mapped green line, the alternate short and longdashed line represents the second intermediate mapped green line, andthe dotted line represents the mapped green line.

[0121] In a step 1103, an upper boundary Bu_(—mapped) of the secondintermediate mapped line in the chroma same as the color M1 iscalculated, and an upper lightness correction value Ad_u is obtained asAd_u=Bu_(—mapped)−Bu. FIG. 12 schematically shows the relation betweenthe upper lightness correction value Ad_u and the upper boundary Bu. Ina step 1104, a lower boundary Bl_(—mapped) of the second intermediatemapped line in the chroma same as the color M1 is calculated, and alower lightness correction value Ad_l is obtained asAd_l=Bl_(—mapped)−Bl. FIG. 12 schematically shows the relation betweenthe lower lightness correction value Ad_l and the lower boundary Bl.

[0122] In a step 1105, an input/output function p(•) for mapping oflightness adjustment is given from the above four parameters. In case ofgiving the input/output function p(•), it is required to satisfyfollowing conditions. Here, symbol L_(Bl) denotes the lightness of lowerboundary Bl, symbol L_(Blm) denotes the lightness of the lower boundaryBl_(—mapped), symbol L_(BU) denotes the lightness of the upper boundaryBu, and symbol L_(Bum) denotes the lightness of the lower boundaryBl_(—mapped).

[0123] The above necessary conditions are as follows. Namely, thesupport of p(•) is [L_(Bl), L_(Bu)], P(•) increases monotonously on thesupport, p(B_(Bl))=B_(Blm), p(L_(Bu))=L_(Bum), p(•) is at least C1continuousness, p′(L_(Bl))=α(α>0, α is a constant to control thecompression, α is determined for each hue according to the lowerlightness correction value Ad_l (α≦1 if Ad_1 is positive, while a α>1 ifAd_1 is negative)), and p′(L_(Bu))=β(β>0, β is a constant to control thecompression, is determined for each hue according to the upper lightnesscorrection value Ad_u (β≧1 if Ad_u is positive, while β≦1 if Ad_u isnegative)).

[0124] The input/output function p(•) is calculated so as to satisfy theabove conditions. Further, in order to preserve the lightness at theintermediate part of the support as much as possible, the input/outputfunction p(•) is calculated such that a lightness change quantitydecreases as much as possible. Here, FIGS. 13A and 13B show an exampleof the input/output function p(•) in the present embodiment.

[0125] Finally, in a step 1106, by using the input/output function p(•)obtained in the step 1105, lightness Lm_(—mapped) after the mapping ofthe color M1 is obtained with respect to lightness Lm before themapping, as Lm_(—mapped)=p(Lm). Thus, the mapping to adjust thelightness is performed.

[0126] By the lightness adjustment mapping operation in the step 504,the area surrounded by the first intermediate mapped line is mapped intothe area surrounded by the second intermediate mapped line. FIG. 14shows an example of the mapping on the green face. In FIG. 14, thealternate short and long dashed line represents the first intermediatemapped green line and the mapping result of the chroma-lightness lociexplained in the step 502, the solid line represents the secondintermediate mapped green line and the result obtained by the lightnessmapping to the mapping result of the chroma-lightness loci, and thedotted line represents the mapped green line.

[0127] In the following, the chroma mapping operation in the step 505will be explained in detail with reference to a flow chart shown in FIG.15.

[0128] In a step 1501, in the hue of a color M2 being the mappingtarget, a boundary (color) Bp of the mapped line in the lightness sameas the color M2 is calculated. In a step 1502, a boundary (color) Bi ofthe second intermediate mapped line in the lightness same as the colorM2 is calculated. FIG. 16 schematically shows the relation among thecolor M2, the color Bp and the color Bi on the green face. In FIG. 16,the solid line represents the second intermediate mapped green line, andthe dotted line represents the mapped green line.

[0129] In a step 1503, an input/output function q(•) for mapping ofcolor gamut correction is given from the color Bp and the color Bicalculated in the above steps. Here, in a case where symbol c_(p)denotes chroma of the color Bp and symbol c_(i) denotes chroma of thecolor Bi, the input/output function q(•) is required to satisfyfollowing conditions.

[0130] Namely, the support of q(•) is [0, c_(i)], q(0)=0,q(c_(i))=c_(p), q′(0)=1, q′(c_(i))=γ (γ>0), and q′(x)≠0 (0≦x≦c_(i)). Thesymbol γ is the value to control enlargement ratio/compression ratio ofthe chroma correction in the vicinity of the maximum chroma, and thisvalue is automatically determined. However, in case of c_(i)>c_(p), γ≦1is given, and the mapping by the input/output function q(•) is thecompression operation. On the other hand, in case of c_(i)≦c_(p), γ≧1 isgiven, and the mapping by the input/output function q(•) is theexpansion (or decompression) operation. FIG. 17A shows an example of theinput/output function q(•) in case of c_(i)≦c_(p) (i.e., the expansionoperation), and FIG. 17B shows an example of the input/output functionq(•) in case of c_(i)>c_(p) (i.e., the compression operation).

[0131] In a step 1504, the chroma of the color M2 is converted by usingthe input/output function q(•) obtained in the step 1503. If symbolC_(org) denotes chroma of the color M2 and symbol c_(mod) denotes chromaof the color M2 after the conversion, c_(mod)=q(c_(org)) is given.

[0132] By the chroma mapping operation in the step 504, the areasurrounded by the second intermediate mapped line is mapped into thearea surrounded by the mapped line. FIG. 18 shows an example of themapping on the green face. In FIG. 18, the alternate short and longdashed line represents the second intermediate mapped green line and thelightness mapping result of the chroma-lightness loci explained in thestep 503, and the solid line represents the mapped green line and theresult obtained by the chroma mapping to the lightness mapping result ofthe chroma-lightness loci.

[0133] Finally, in a step 506, the hue is appropriately adjusted on thebasis of the information obtained by the mapping parameter calculationdevice 206.

[0134] As above, the mapping of the internal sample points in the step303 was described in detail. In the step 303 of the present embodiment,the algorithm on the premise that the mapping to be originally performedon the three-dimensional space has been reduced to the mapping on thetwo-dimensional space was explained. However, it is of course possibleto perform the mapping on the three-dimensional space as it is.

[0135] In the following, an example of the method to define the surfacegradation line in the step 304 will be described with reference to FIG.19.

[0136]FIG. 19 shows a state that the surface gradation lines is definedin a case where the number of surface sample points belonging to eachface is the identical. Here, a gradation line Li in FIG. 22 representsthe surface gradation line connecting the surface sample point on thered face and the surface sample point on the yellow face with eachother. Symbol Ri denotes a surface sample point on the red face, and anindex i is given to this surface sample point in the order of higherlightness. Symbol Yi denotes a surface sample point on the yellow face,and an index i is given to this surface sample point in the order ofhigher lightness. As apparent from the drawings, in the presentembodiment, the sample points having the identical index number areconnected to define the surface gradation line. Further, the surfacegradation line has following R, G and B values.

R=(1−t)Rri+tRyi

G=(1−t)Gri+tGyi

B=(1−t)Bri+tByi

[0137] Here, symbols R, G and B respectively denote the R, G and Bvalues of the surface gradation line, symbols Rri, Gri and Brirespectively denote the R, G and B values of the sample point Ri,symbols Ryi, Gyi and Byi respectively denote the R, G and B values ofthe sample point Yi, and 0≦t≦1.

[0138] Namely, the surface gradation line is obtained by representing inthe L*a*b* color space the line connecting the surface sample points onthe RGB color space.

[0139] However, in addition to the above expression of the presentembodiment, the surface gradation line can be represented in variousdefinition methods. Thus, any inconvenience does not occur even if thedefinition method different from that shown in the present embodiment isused. Further, any inconvenience does not occur even if the number ofsurface sample points belonging to each face is not the identical.

[0140] In the mapping of the surface gradation line in the step 305, thesurface gradation line of FIG. 19 is, e.g., shown in FIG. 20. Further,as described also in the first embodiment, it should be noted that themapping result of the surface gradation line is not necessarily locatedon the surface of the printer color reproduction gamut.

[0141] In the following, an example of the method to define the internalgradation line in the step 306 will be described with reference to FIG.21.

[0142]FIG. 21, a gradation line Lin_ij represents the internal gradationline connecting an internal sample point Rin_i on the red face and aninternal sample point Yin_j on the yellow face with each other. Here,the internal gradation line has following R, G and B values.

R=(1−t)Rri+tRyj

G=(1−t)Gri+tGyj

B=(1−t)Bri+tByj

[0143] Here, symbols R, G and B respectively denote the R, G and Bvalues of the internal gradation line, symbols Rri, Gri and Brirespectively denote the R, G and B values of the sample point Rin_i,symbols Ryj, Gyj and Byj respectively denote the R, G and B values ofthe sample point Yin_j, and 0≦t≦1.

[0144] Namely, as well as the surface gradation line, the internalgradation line is obtained by representing in the L*a*b* color space theline connecting the surface sample points on the RGB color space.

[0145] Although the mapping of the internal gradation line in the step307 is influenced from either one or both the surface gradation line andthe adjacent internal gradation line, such the influence is eased inproportion to the distance between the influenced surface gradation lineand the influenced internal gradation line. For example, the internalgradation lines shown in FIG. 21 are mapped as shown in FIG. 22.

[0146]FIGS. 23 and 24 show an example of gradation line control based ona control point. Concretely, FIG. 23 shows that a control point Cnt isdetermined on the gradation line Lin_55, and FIG. 24 shows thecoordinates at which the control point Cnt of FIG. 23 is mapped. Thus,the mapping of the internal gradation line Lin_55 varies according tothe mapping of the control point Cnt. Also, the adjacent internalgradation line varies due to influence of the mapping variation of theinternal gradation line Lin_55, but such the influence is eased inproportion to the distance from the internal gradation line Lin_55. Inthe present embodiment, the internal gradation line is controlled to bepassed through the control point, but the internal gradation line is notnecessarily passed through the control point in such as case as theB-Spline curve is used.

[0147] As well as the first embodiment, it should be noted that themapping is controlled such that the mapping result of the surface samplepoints is sure to be located inside the printer color reproductiongamut.

[0148] As described above, according to the present embodiment, sincethe gamut mapping is controlled on the basis of the six hues of primarycolors, it is possible to perform intuitive control.

[0149] Further, according to the present embodiment, since the prior artis applied to the mapping of the six hue faces, it is possible to useconventional know-how and also take adjustment with the conventionalgamut mapping.

[0150] Third Embodiment

[0151] In the third embodiment, how to take the surface sample pointsand the internal sample points in the second embodiment is devised, andalso how to take the surface gradation line and the internal gradationline in the second embodiment is devised, whereby the labor in the colordesign is further reduced, and the control is made further easy to begrasped intuitively.

[0152] It should be noted that the third embodiment is obtained bymodifying the surface sample points and the internal sample points inthe operation algorithm of the color gamut mapping device 207 in thesecond embodiment. For this reason, the parts overlapping with the partsin the second embodiment are omitted, and only the different parts willbe described.

[0153] In the following, how to determined the sample point in the step301 of the flow chart shown in FIG. 3 will be described in detail.

[0154] In the present embodiment, how to determine the surface andinternal sample points distributed on the six faces, i.e., red, green,blue, cyan, magenta and yellow faces, will be explained. Incidentally,of course, there is no problem even if a sample point which is notdistributed on any of the above six faces (i.e., not satisfying any ofthe conditions A1 to A12 and B1 to B6 in the second embodiment andlater-described conditions) exists.

[0155] In the present embodiment, the sample point is determined not inthe L*a*b* color space but in the RGB color space. Here, as to R, G andB values capable of being taken at the sample point, it is defined todetermine the R, G and B values in the same discrete step. Namely, aseach of the R, G and B values, it is defined to take any of discretevalues shown in FIG. 25. Further, the surface sample point satisfies anyof the 12 conditions A1 to A12, and the internal sample point satisfiesany of the six conditions B1 to B6.

[0156]FIG. 26 shows the distributions of the surface sample points andthe internal sample points on the RGB color space, by using the red faceand the cyan face as examples. Concretely, FIG. 26 shows the sectionalplane which is obtained by sectioning the color reproduction gamut onthe RGB color space through three (white, red and black) points. In FIG.26, the upper left point (255, 255, 255) represents white, and lowerright point (0, 0, 0) represents black. The dotted line represents agray axis which varies from the white point (255, 255, 255) to the blackpoint (0, 0, 0) on the (R, G, B) coordinates. Symbol Ri denotes asurface sample point on the red face, symbol Ci denotes a surface samplepoint on the cyan face, and an index i is given to such the surfacesample point in the order of higher lightness. Further, symbol Rin_idenotes an internal sample point on the red face, and symbol Cin_jdenotes an internal sample point on the cyan face. The index number rulein the internal sample points is as follows.

[0157] First, with respect to the internal sample points having themaximum hue component on the hue face in question, the index numbers aresequentially given to these points in the order of higher lightnesssample points. Namely, on the red face, in the internal sample points ofwhich the red components are given as d₁, the index numbers aresequentially given to these points in the order of higher lightnesssample points. Further, on the cyan face, in the internal sample pointsof which the green components and the blue components are given as d₁,the index numbers are sequentially given to these points in the order ofhigher lightness sample points.

[0158] Subsequently, with respect to the internal sample points havingthe large hue components, the index numbers are sequentially given tothese points in the order of higher lightness sample points. Namely, onthe red face, in the internal sample points of which the red componentsare given as d₂, the index numbers are sequentially given to thesepoints in the order of higher lightness sample points. Further, on thecyan face, in the internal sample points of which the green componentsand the blue components are given as d₂, the index numbers aresequentially given to these points in the order of higher lightnesssample points. After then, the index numbers are given to all theinternal sample points in the same manner as above, whereby thedistributions as shown in FIG. 26 can be obtained. Besides, on thegreen, blue, magenta and yellow faces, the index numbers are given tothe internal sample points in the same manner as above.

[0159] In the following, the method to define the surface gradation linein the step 304 will be explained.

[0160] In the present embodiment, the surface gradation line is definedby connecting, with a line on the RGB color space, the surface samplepoints of which the index numbers are the identical respectively on theadjacent hue faces. For example, the surface gradation line between thered face and the yellow face has following R, G and B values.

R=(1−t)Rri+tRyi

G=(1−t)Gri+tGyi

B=(1−t)Bri+tBRyi

[0161] Here, symbols R, G and B respectively denote the R, G and Bvalues of the surface gradation line, symbols Rri, Gri and Brirespectively denote the R, G and B values of the sample point Ri,symbols Ryi, Gyi and Byi respectively denote the R, G and B values ofthe sample point Yi, and 0≦t≦1.

[0162] In the following, the method to define the internal gradationline in the step 306 will be explained.

[0163] In the present embodiment, the internal gradation line is definedby connecting, with a line on the RGB color space, the internal samplepoints of which the index numbers are the identical respectively on theadjacent hue faces. For example, the internal gradation line between thered face and the yellow face has following R, G and B values.

R=(1−t)Rri+tRyi

G=(1−t)Gri+tGyi

B=(1−t)Bri+tBRyi

[0164] Here, symbols R, G and B respectively denote the R, G and Bvalues of the internal gradation line, symbols Rri, Gri and Brirespectively denote the R, G and B values of the sample point Rin_i,symbols Ryi, Gyi and Byi respectively denote the R, G and B values ofthe sample point Yin_i, and 0≦t≦1.

[0165] According to the present embodiment, since how to take the samplepoints and the gradation lines are devised, the mapping control is madefurther easy to be grasped intuitively.

[0166] Other Embodiments

[0167] The present invention also includes a case of supplying a programcode of software for achieving the functions of the above embodiments toa computer (CPU or MPU) in an apparatus or a system connected to variousdevices to operate these devices to achieve the functions of the aboveembodiments, and causing the computer in the apparatus or the system tooperate these devices according to the supplied program codes.

[0168] In this case, the program code of software achieves the functionsof the above embodiments, whereby the program code itself and a meanssuch as a storage medium for storing the program code constitute thepresent invention.

[0169] As the storage medium for storing the program code, e.g., afloppy disk, a hard disk, an optical disk, a magneto-optical disk, aCD-ROM, a magnetic tape, a non-volatile memory card, a ROM or the likecan be used.

[0170] It is needless to say that the program code is included in theembodiments of the present invention not only in the case where thefunctions of the above embodiments are achieved by executing thesupplied program code with the computer, but also in a case where theprogram code cooperates with an OS (operating system) running on thecomputer or other application software to achieve the functions of theabove embodiments.

[0171] Further, it is needless to say that the present inventionincludes a case where the supplied program code is stored in a memoryprovided in a function expansion board inserted in the computer or afunction expansion unit connected to the computer, thereafter, on thebasis of an instruction of the program code, a CPU or the like providedin the function expansion board or the function expansion unit executesa part or all of actual processes, and thus the functions of the aboveembodiments are achieved by such the processes.

[0172] The present invention can be modified in various manner withinthe scope of the following claims.

What is claimed is:
 1. An image processing method by which a color signal located within a first color reproduction gamut represented by a first color system is subjected to mapping conversion into a color signal located within a second color reproduction gamut represented by the first color system, wherein a locus of a change of color in the first color reproduction gamut is represented by a curve, mapping is performed to the curve, and the mapping conversion is performed on the basis of relation of the curves before and after the mapping.
 2. A method according to claim 1, wherein the mapping is performed such that a change rate of the curve is maintained.
 3. A method according to claim 1, wherein the locus of the change of color in the first color reproduction gamut is obtained on the basis of surface sample points in the first color reproduction gamut.
 4. A method according to claim 1, wherein a first gradation line being the curve representing the locus of the change of color in the first color reproduction gamut and a second gradation line in the second color reproduction gamut are obtained, and the mapping conversion of the color signal in the first color reproduction gamut into the color signal in the second color reproduction gamut is performed on the basis of the second gradation line corresponding to the first gradation line relative to the color signal in the first color reproduction gamut.
 5. A method according to claim 1, wherein the curve is obtained by using at least one of a B-Spline curve, a rational B-Spline curve, a Bezier curve, and a one- or more-dimensional spline curve.
 6. A method according to claim 1, wherein plural first color signals belonging to the first color reproduction gamut are set, the curve is obtained on the basis of the set plural first color signals, and in a subset of the color signals being not an empty set, the color signals being the components of the subset are constrained such that they belong to any of six hue faces of a red face, a green face, a blue face, a cyan face, a magenta face and an yellow face.
 7. A method according to claim 1, wherein, in the mapping conversion, hue adjustment to adjust two-dimensional mapping and a hue component on a lightness-chroma plane according to the second color reproduction gamut is performed to the color signal in the first color reproduction gamut.
 8. A method according to claim 4, wherein, in the mapping conversion, the color signal is extracted from the second gradation line in accordance with a ratio of hue angle of the color signal on the first gradation line.
 9. A method according to claim 4, wherein, in the mapping conversion, the color signal is extracted from the second gradation line in accordance with a ratio of the length of the first gradation line and the length from the edge point of the first gradation line to the color signal being the target of the mapping conversion result calculation.
 10. An image processing apparatus by which a color signal located within a first color reproduction gamut represented by a first color system is subjected to mapping conversion into a color signal located within a second color reproduction gamut represented by the first color system, wherein a locus of a change of color in the first color reproduction gamut is represented by a curve, mapping is performed to the curve, and the mapping conversion is performed on the basis of relation of the curves before and after the mapping.
 11. A storage medium which computer-readably stores a program to achieve an image processing method by which a color signal located within a first color reproduction gamut represented by a first color system is subjected to mapping conversion into a color signal located within a second color reproduction gamut represented by the first color system, wherein the program by which a locus of a change of color in the first color reproduction gamut is represented by a curve, mapping is performed to the curve, and the mapping conversion is performed on the basis of relation of the curves before and after the mapping. 